[RFC PATCH 3/3] hw/virtio: Have virtqueue_get_avail_bytes() pass caches arg to callees

["Philippe Mathieu-Daudé" <philmd@redhat.com>]

Both virtqueue_packed_get_avail_bytes() and
virtqueue_split_get_avail_bytes() access the region cache, but
their caller also does. Simplify by having virtqueue_get_avail_bytes
calling both with RCU lock held, and passing the caches as argument.

Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
---
RFC because I'm not sure this is safe enough
---
 hw/virtio/virtio.c | 29 ++++++++++++-----------------
 1 file changed, 12 insertions(+), 17 deletions(-)

diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
index 3a1f6c520cb..8237693a567 100644
--- a/hw/virtio/virtio.c
+++ b/hw/virtio/virtio.c
@@ -984,28 +984,23 @@ static int virtqueue_split_read_next_desc(VirtIODevice *vdev, VRingDesc *desc,
     return VIRTQUEUE_READ_DESC_MORE;
 }
 
+/* Called within rcu_read_lock().  */
 static void virtqueue_split_get_avail_bytes(VirtQueue *vq,
                             unsigned int *in_bytes, unsigned int *out_bytes,
-                            unsigned max_in_bytes, unsigned max_out_bytes)
+                            unsigned max_in_bytes, unsigned max_out_bytes,
+                            VRingMemoryRegionCaches *caches)
 {
     VirtIODevice *vdev = vq->vdev;
     unsigned int max, idx;
     unsigned int total_bufs, in_total, out_total;
-    VRingMemoryRegionCaches *caches;
     MemoryRegionCache indirect_desc_cache = MEMORY_REGION_CACHE_INVALID;
     int64_t len = 0;
     int rc;
 
-    RCU_READ_LOCK_GUARD();
-
     idx = vq->last_avail_idx;
     total_bufs = in_total = out_total = 0;
 
     max = vq->vring.num;
-    caches = vring_get_region_caches(vq);
-    if (!caches) {
-        goto err;
-    }
 
     while ((rc = virtqueue_num_heads(vq, idx)) > 0) {
         MemoryRegionCache *desc_cache = &caches->desc;
@@ -1124,32 +1119,28 @@ static int virtqueue_packed_read_next_desc(VirtQueue *vq,
     return VIRTQUEUE_READ_DESC_MORE;
 }
 
+/* Called within rcu_read_lock().  */
 static void virtqueue_packed_get_avail_bytes(VirtQueue *vq,
                                              unsigned int *in_bytes,
                                              unsigned int *out_bytes,
                                              unsigned max_in_bytes,
-                                             unsigned max_out_bytes)
+                                             unsigned max_out_bytes,
+                                             VRingMemoryRegionCaches *caches)
 {
     VirtIODevice *vdev = vq->vdev;
     unsigned int max, idx;
     unsigned int total_bufs, in_total, out_total;
     MemoryRegionCache *desc_cache;
-    VRingMemoryRegionCaches *caches;
     MemoryRegionCache indirect_desc_cache = MEMORY_REGION_CACHE_INVALID;
     int64_t len = 0;
     VRingPackedDesc desc;
     bool wrap_counter;
 
-    RCU_READ_LOCK_GUARD();
     idx = vq->last_avail_idx;
     wrap_counter = vq->last_avail_wrap_counter;
     total_bufs = in_total = out_total = 0;
 
     max = vq->vring.num;
-    caches = vring_get_region_caches(vq);
-    if (!caches) {
-        goto err;
-    }
 
     for (;;) {
         unsigned int num_bufs = total_bufs;
@@ -1250,6 +1241,8 @@ void virtqueue_get_avail_bytes(VirtQueue *vq, unsigned int *in_bytes,
     uint16_t desc_size;
     VRingMemoryRegionCaches *caches;
 
+    RCU_READ_LOCK_GUARD();
+
     if (unlikely(!vq->vring.desc)) {
         goto err;
     }
@@ -1268,10 +1261,12 @@ void virtqueue_get_avail_bytes(VirtQueue *vq, unsigned int *in_bytes,
 
     if (virtio_vdev_has_feature(vq->vdev, VIRTIO_F_RING_PACKED)) {
         virtqueue_packed_get_avail_bytes(vq, in_bytes, out_bytes,
-                                         max_in_bytes, max_out_bytes);
+                                         max_in_bytes, max_out_bytes,
+                                         caches);
     } else {
         virtqueue_split_get_avail_bytes(vq, in_bytes, out_bytes,
-                                        max_in_bytes, max_out_bytes);
+                                        max_in_bytes, max_out_bytes,
+                                        caches);
     }
 
     return;
-- 
2.31.1